Aberrations in patterns of tRNA methylation and in the activities of the tRNA methyl-transferases in neoplastic cells are well documented. However, little is known of the role of methylated bases in tRNA, the implications of altered methylation for the growth of neoplastic cells, and the factors which modulate activity of the various methyltransferases. Our research is designed to examine the effect of several base methylations which are characteristic of eucaryotic tRNA on the structure and function of tRNAs, and to examine the effect of impaired tRNA methylation on the growth of mammalian cells. It is also designed to examine the parameters which influence the capacity of individual methyltransferases to modify various tRNAs. The proposed experiments will utilize several highly purified mammalian tRNA methyltransferases to modify bacterial tRNAs. We will then examine the effect of these modifications on the tRNA functions in protein synthesis and on the stability and tertiary structure of the nucleic acid as seen by NMR. We also propose to use methyltransferase inhibitors to suppress selected tRNA methylations in cell culture. This will permit, for the first time, an examination of the effect of specific hypomethylations on eucaryotic cell function as well as make available a source of methylatable mammalian tRNA for in vitro studies. Investigations of the factors controlling the rate and extent of methylatable mammalian tRNA for in vitro studies. Investigations of the factors controlling the rate and extent of methylation by purified methyltransferases will include examination of the mechanism of tRNA methylation reactions, the effect of substrate and product levels, the role of polyamines and the influence of prior methylations of the tRNA.